This invention relates to improved glyphosate formulations.
Glyphosate (N-phosphonomethylglycine) is well known as a foliage acting herbicide. In the free acid form, glyphosate has low water solubility, and because of this, commercial formulations contain a water-soluble salt of glyphosate. For example, in Roundup.RTM. herbicide, glyphosate is present as the water-soluble mono-isopropylamine salt.
Several studies on the effect of surfactants on the herbicidal activity of the monoisopropylamine salt of glyphosate are reported in the literature. For example, Turner and Loader, Weed Research, 1980, Vol 20, 139-146 reported that fatty amine ethoxylates having a hydrophile-lipophile balance of 17, are generally the most effective in increasing the herbicidal activity of solutions of Roundup.RTM. herbicide. In the same publication, the authors state that with spray solutions containing ammonium sulfate, responses to surfactants were different, with lipophilic surfactants, for example fatty amine ethoxylates having a hydrophile-lipophile balance of 6, usually having greater effects.
In 1985 BCPC Monogram No. 28 Symposium on Application and Biology "Studies with Alternative Glyphosate Formulations", Turner and Tabbush describe the results of some trials with glyphosate acid formulated as a foliage spray. In summarizing the results, they state that glyphosate acid had relatively little activity unless surfactants and/or ammonium sulfate was added, but that when this was done, its phytotoxicity was equivalent to that of Roundup.RTM. herbicide. There is an observation that glyphosate acid is much more soluble in a solution of a tertiary amine from tallow containing 15 mols of ethylene oxide per mol of amine than in pure water.
U.S. Pat. No. 4,612,034 describes herbicidal formulations comprising mixtures of the isopropylamine salt of glyphosate and a potentiating amount of a specified class of thiocyanates including ammonium thiocyanate.
In the experiments described in 1985 BCPC Monogram No. 28 on the preparation of salts of glyphosate or the solubilization of glyphosate acid with ethoxylated fatty acid amines, the ethoxylated fatty acid amine surfactant was used in an excess of at least five parts by weight per part by weight of glyphosate acid. While one experiment described in Weed Research, 1980, Vol 20, 139-146, uses a solution containing less surfactant than glyphosate (as Roundup.RTM. herbicide, which itself contains a significant amount of surfactant) it was applied by a controlled drop technique at 20 l/ha. For experiments in which solutions were sprayed by conventional techniques at normal farm application rates of about 200 l/ha, however, the solutions contained about twice as much surfactant as glyphosate.
In 1981 D. J. Turner in the Proceedings of the Conference on Grass Weeds in Cereals in the United Kingdom Conference presented a reading entitled "The Effect of Additives on the Control of Agropyron Pepens with Glyphosate". He reported the effect of using mixtures of ammonium sulfate and Ethomeen C/12 surfactant which is an ethoxylated derivative of cocoamine containing an average of about 2 ethoxy groups. Turner's compositions contained a large amount of ammonium sulfate in relation to the amount of glyphosate. The lowest ratio of ammonium sulfate to glyphosate tested by Turner has been calculated to be 3.75:1. At the high ratios of ammonium sulfate to glyphosate disclosed by Turner it becomes impractical to formulate aqueous solutions of glyphosate salt, surfactant and ammonium sulfate except at glyphosate acid equivalent (a.e.) concentrations below about 90 g/l. Turner's compositions cannot therefore be formulated as aqueous concentrates at a glyphosate loading which is high enough to be commercially attractive in most agricultural markets.
In the investigations leading to the present invention, we worked at conventional spray rates (around 200 l/ha), and with solutions containing lower surfactant to glyphosate ratios and/or lower ammonium sulfate to glyphosate ratios than those disclosed in the prior art for solutions sprayed at those rates. We have found that with our solutions, better results are obtained under most conditions with the lipophilic fatty amine ethoxylates than with the more hydrophilic fatty amine ethoxylates hitherto thought to be optimum. This is so, whether or not the solution also contains ammonium sulfate. These observations are surprising in view of the prior art which suggests that the lipophilic surfactants would not be the surfactants of choice except in the presence of rather high amounts of ammonium sulfate.
Nowhere in the prior art has it been discovered that, at low surfactant to glyphosate (a.e.) ratios (about 1.75:1 or lower), aqueous formulations of glyphosate with an alkoxylated amine surfactant having about 8 or fewer alkoxy groups, either substantially free of inorganic ammonium salt or with a ratio of such salt to glyphosate (a.e.) lower than about 3.6:1, provide better performance than otherwise similar formulations, hitherto taught to be optimal, with an alkoxylated amine surfactant having about 15 alkoxy groups. The present invention unexpectedly provides aqueous concentrate glyphosate formulations with significantly enhanced herbicidal activity over prior art formulations. What is particularly surprising is that the class of surfactants used at low surfactant to glyphosate ratios in compositions of the invention is taught by the prior art (see the Turner references cited above and also Wyrill and Burnside, Weed Science Vol. 25 (1977), pp. 275-287) to be of relatively poor efficacy when tested at high surfactant to glyphosate ratios.
A feature of the present invention is that the amount of alkoxylated amine surfactant relative to total glyphosate can be reduced significantly below the ratio disclosed in the prior art for conventional spray solutions having no or low amounts of inorganic ammonium salt, while enhancing the herbicidal activity per unit of glyphosate by comparison with similar (prior art) solutions in which the alkoxylated amine surfactant has about 15 alkoxy groups instead of about 8 or fewer in solutions of the invention.